Coated articles are known in the art for use in window applications such as insulating glass (IG) window units, vehicle windows, and/or the like. Example non-limiting low-emissivity (low-E) coatings are illustrated and/or described in U.S. Pat. Nos. 6,723,211; 6,576,349; 6,447,891; 6,461,731; 3,682,528; 5,514,476; 5,425,861; and 2003/0150711, the disclosures of which are all hereby incorporated herein by reference.
In certain situations, designers of coated articles with low-E coatings often strive for a combination of high visible transmission, substantially neutral color, low emissivity (or emittance), low sheet resistance (Rs), and good durability. High visible transmission for example may permit coated articles to be more desirable in applications such as vehicle windshields or the like, whereas low-emissivity (low-E) and low sheet resistance (Rs) characteristics permit such coated articles to block significant amounts of IR radiation so as to reduce for example undesirable heating of vehicle or building interiors. It is often difficult to obtain high visible transmission and adequate solar control properties, combined with good durability because materials used to improve durability often cause undesirable drops in visible transmission and/or undesirable color shifts of the product upon heat treatment.
Coated articles used in windows (e.g., vehicle windows, architectural windows, or the like) often must be heat treated (e.g., thermally tempered, heat bent and/or heat strengthened). However, a problem which frequently occurs with heat treatment is sodium (Na) migration into the coating from the glass substrate. For instance, during heat treatment (HT) sodium tends to migrate from the glass substrate into the coating and can severely damage the infrared (IR) reflecting layer(s) (e.g., silver layer or layers) if such migrating sodium reaches the same.
It has been proposed to use sputter-deposited silicon nitride as a base layer for coatings in an effort to reduce sodium migration which can occur during heat treatment. However, silicon nitride formed only by sputtering is problematic in certain respects. FIG. 1 of the instant application, for example, illustrates that sputter-deposited silicon nitride layers realize an increase in voids defined therein as sputter deposition rate increases (the data in FIG. 1 is from silicon nitride deposited only via sputtering in a known manner). A large number of voids in a base layer of silicon nitride can be undesirable since sodium can migrate through the layer during heat treatment via such voids, and attack the IR reflecting layer(s) leading to structural damage and/or coating failure. For example, such sodium attacks can increase haze in the heat treated coated article and/or can adversely affect optical characteristics of the coated article following heat treatment.
U.S. Pat. No. 5,569,362 discloses a technique for ion beam treating a coating using at least oxygen in order to densify the same. However, the '362 Patent is unrelated to nitrogen doping Si3N4, is unrelated to heat treated products and problems which may arise upon heat treatment, and is undesirable in that it's use of significant amounts of oxygen in the ion beam renders treated layers and layers adjacent thereto susceptible to significant undesirable change upon heat treatment.
In view of the above, it will be apparent to those skilled in the art that there exists a need for a method of making a coated article with an ion beam treated layer in a manner suitable to at least one of: (a) improve optical characteristics of the coated article such as haze reduction and/or coloration following optional heat treatment; (b) improve durability of the coated article; and/or (c) reduce the potential for significant changing of optical characteristics of the coating upon heat treatment. There also exists a need for corresponding coated articles.